REBCO (RE = rare earth) based high temperature superconducting (HTS) wires are now being utilized for the development of electric and electromagnetic devices for various industrial, scientific and medical applications. In the last several years, the increasing efforts in using the so-called second generation (2G) HTS wires for some of the applications require a further increase in their engineering current density (Je). The applications are those typically related to high magnetic fields where the higher Je of a REBCO wire, in addition to its higher irreversibility fields and higher mechanical strength, is already a major advantage over other superconducting wires. An effective way to increase the Je is to decrease the total thickness of a wire, for which using a thinner substrate becomes an obvious and attractive approach. By using our IBAD-MOCVD (ion beam assisted deposition-metal organic chemical vapor deposition) technology we have successfully made 2G HTS wires using a Hastelloy® C276 substrate that is only 30 μm in thickness. By using this thinner substrate instead of the typical 50 μm thick substrate and with a same critical current (Ic), the Je of a wire can be increased by 30% to 45% depending on the copper stabilizer thickness. In this paper, we report the fabrication and characterization of the 2G HTS wires made on the 30 μm thick Hastelloy® C276 substrate. It was shown that with the optimization in the processing protocol, the surface of the thinner Hastelloy® C276 substrate can be readily electropolished to the quality needed for the deposition of the buffer stack. Same in the architecture as that on the standard 50 μm thick substrate, the buffer stack made on the 30 μm thick substrate showed an in-plane texture with a Δϕ of around 6.7° in the LaMnO3 cap layer. Low-temperature in-field transport measurement results suggest that the wires on the thinner substrate had achieved equivalent superconducting performance, most importantly the Ic, as those on the 50 μm thick substrate. It is expected the 2G HTS wires made on the 30 μm thick Hastelloy® C276 substrate, the thinnest and with the highest Je to date, will greatly benefit such applications as high field magnets and high current cables.
Next generation particle accelerators and fusion machines will greatly benefit from the development of low-inductance magnets capable of generating magnetic fields in excess of 16 T. Such magnets require high-temperature superconductors capable of carrying very high currents exceeding 5 kA at current densities of 400-600 A mm −2 , such as Conductor on Round Core (CORC ® ) cables and wires wound from RE-Ba 2 Ca 3 O 7-δ (ReBCO, Re=rare earth) coated conductor tapes. CORC ® wires containing ReBCO tapes with 30 μm thick Hastelloy ® substrates have previously been demonstrated as a viable high-field magnet conductor that can be produced at long lengths. Further improvement of the performance and flexibility of CORC ® wires would benefit from the development of ReBCO tapes with even thinner substrates. SuperPower Inc. recently demonstrated ReBCO tapes based on 25 μm thick Hastelloy ® substrates that allow the development of thinner and more flexible CORC ® wires that meet the stringent performance requirements of high-field magnets. Several tapes containing 25 μm thick substrates were produced and analyzed, exhibiting critical current and cabling performance in-line with the current production level tapes with 30-50 μm thick substrates. Tape critical current was measured at 4.2 K and applied magnetic fields up to 31.2 T. Several CORC ® wires incorporating these tapes were manufactured by Advanced Conductor Technologies using similar winding procedures that previously resulted in high-quality magnet-grade CORC ® wires based on tapes with 30 μm thick substrates. The CORC ® wires were tested in an applied magnetic field up to 12 T after bending to a 63 mm diameter. A critical current as high as 6231 A (12 T, 4.2 K) was measured with an engineering current density (J e ) of 678 A mm −2 , which extrapolates to over 450 A mm −2 at 20 T and is the highest current density reported in a CORC ® conductor to date. The combination of ReBCO tapes produced using 25 μm thick substrates and the ability to wind them into longlength, high-quality CORC ® magnet wires brings the development of low-inductance accelerator and fusion magnets that operate at magnetic fields exceeding 20 T closer to fruition.
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